Field of the Invention
The present invention relates to a voltage generation circuit capable of monitoring an output voltage and generating a required voltage at the same time, and in particular it relates to a voltage generation circuit generating the required voltage for operation of a semiconductor device comprising a flash memory and other integrated circuits.
Description of the Related Art
As semiconductor design scales down in dimensions, the operation voltages and the power-supply voltages of semiconductor devices are reduced accordingly. For example, the power-supply voltage outside a semiconductor device is decreased from 3.3 V to either 2.5 V or 1.8 V. On the other hand, the internal circuits of semiconductor devices may require multiple voltage supplies, including voltage for driving transistors, and voltage applied to a substrate and well regions, which are higher than the external power-supply voltage. Therefore, semiconductor devices have voltage-boosting circuits to raise external power-supply voltages to the required voltages and level shift circuits.
Japanese laid-open patent application No. 2012-244660 discloses a NAND-type flash memory with a voltage-boosting circuit. The voltage-boosting circuit comprises a charge pump. The current consumption and layout (area) of the voltage-boosting circuit are reduced by decreasing number of stages in the charge pump. Japanese laid-open patent application No. 2013-157053 also discloses a NAND-type flash memory with a voltage generation circuit. The voltage generation circuit has a charge pump circuit and a clamp circuit. The clamp circuit monitors output voltages of the charge pump circuit to control the charge pump circuit. The clamp circuit has a first resistor device, a second resistor device, a first capacitor device, a second capacitor device, a switch device and a comparator. One input of the comparator is connected to connection portions of the first and second resistor devices, and the other input of the comparator is input by a reference voltage. In addition, the first capacitor device is connected between the output of the charge pump circuit and one input of the comparator. When the output of the charge pump circuit is connected to a load, the second capacitor device is connected to one input of the comparator through the switch device so as to stabilize the boosted voltage.